Drivers and consequences of phenological change at high altitudes
Collaborators: Dr. David Inouye (RMBL) , Dr. Rebecca Irwin (NCSU)
Our climate is changing rapidly, and the effects of these changes are expected to be particularly strong at high altitudes. We are working at the Rocky Mountain Biological Laboratory (RMBL) to document: the timing of flowering (flowering phenology) of the plant community in montane meadows; the abundance, diversity, and phenology of the bee community, and climate variables. Our now >46-year dataset on flowering phenology and >12-year dataset on bees allows us to address a wide variety of questions about the effects of climate on phenology, effects of climate change, the links between plants and pollinators, and community-level responses to climate. |
Measuring and modeling the ecological consequences of associational effects
Collaborators: Dr. Stacey Halpern (Pacific University) and Dr. Peter Hambäck (Stockholm University); Funded by: NSF DEB
Associational effects (AE) occur when neighboring resource organisms influence each other’s interactions with consumers or mutualists. In the context of interactions between plants and insect herbivores, AE are the effects of neighboring plants on a focal plant’s damage from herbivores. Because herbivores can influence plant growth and reproduction, it has been suggested that AE should influence population-level processes in plant-herbivore systems, including competition and natural selection for resistance. Our goal in this project is to use a combination of mathematical models and empirical work to address whether and how AE influence the outcome of plant interspecific competition (coexistence and/or relative abundance). Work for this project was done in the field at the North Florida Research and Education Center. |
Using Colorado potato beetle responses to predators to maximize pest control
Collaborator: Dr. Jennifer Thaler (Cornell University) ; Funded by USDA
Predators are important contributors to sustainable pest management, although our use of them can be greatly improved. In previously funded AFRI research, we discovered that all beetle pest life-stages are affected by the presence of predators; when predators are present, adults and larvae feed less, and adults lay fewer eggs compared to no-predator controls -- thus, benefiting agriculture. However, parental predator exposure also increases their investment in offspring quality, potentially increasing offspring survival in the face of predation or other stresses. This allows the pests to compensate for their initially reduced densities. To maximize the negative effects of predators on pests, knowledge of both short and long-term effects of predators on pest populations must be integrated. Our goal for this project was to measure the fundamental tradeoff between offspring number and offspring quality for beetles exposed to predators at different life stages. We measured the influence of offspring density and quality on offspring performance and plant damage in stressful environments. We then modeled the consequences for beetle population growth. This research provided insight into how to manipulate prey's responses to predators to maximize suppression of the pest population as it interacts with plant resistance. |
The effect of insect herbivores on plant population dynamics
Collaborator: Dr. Stacey Halpern (Pacific University); Funded by NSF, USDA, and the L'Oreal Foundation
While the importance of competition with other plants is widely recognized, the effect of herbivores on plant populations is more contentious; some contend that insect herbivores have little effect, while others argue that insect herbivores can strongly limit plant population size. The persistence of these conflicting opinions indicates that the nature and prevalence of herbivore effects remains unresolved. Our goal in this project was to fully characterize herbivore effects on the population dynamics of a plant by incorporating effects of herbivores on both population growth rates and density dependence (change in growth rate with plant density) across the life cycle of the plant. We used a combination of density manipulation experiments and demographic modeling to investigate whether and how insect herbivores affect population dynamics in the perennial herb Solanum carolinense. |
Induced resistance and herbivore population dynamics
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Many plants are able to increase their level of resistance to herbivores in response to herbivore damage (induced resistance). We were interested in the consequences of induced versus unchanging (or constitutive) resistance strategies for herbivore population dynamics since induced resistance is a potential source of density-dependent regulation for herbivores.
Our goal for this study was to provide experimental evidence that plant resistance can influence herbivore populations over longer than one season. We used a density manipulation experiment and model fitting to examine the effects of constitutive and induced resistance on herbivore dynamics over both the short and long-term. The results of this study suggest that induced and constitutive resistance can differ in their effects on herbivore populations even in a relatively complex system. |
The influence of variance in quality within plant populations on herbivore dynamics and spatial distributions
Collaborator: Dr. Stacey Halpern (Pacific University)
The quality of individual plants as food for herbivores (and thus the mean quality of plant populations or communities) can influence both individual herbivores and herbivore populations. However, assemblages of plants vary not only in mean quality, but also in the variance around that mean (CV). In this project, we looked at how aphid movement responses to individual plant quality are affected by population variance in plant quality, and used longer-term experiments to follow aphid population dynamics on plant populations with different levels of quality variance. To do so, we used both field experiments and models. This research allowed for critical examination of the hypothesis that agricultural mixtures of plant varieties (genotypes) should host lower pest populations than monocultures. |
Effects of fire and land management in the Apalachicola National Forest on plants and insects
Effects of patchy disturbance on the distribution and pollination of a rare endemic plant
We examined the effect of disturbance in the form of gopher mounds on the recruitment and performance of Mimulus angustatus at the Las Posadas State Forest, Napa Co, CA. Mimulus produces a tiny rosette and then a variable number of flowers that are huge relative to the rest of the plant. Through observations and experiments we have found that this Mimulus is far more common on gopher mounds (or in other disturbed areas), germinates at far greater rates on mounds, and has more and larger flowers on mounds. Flowers on mounds also receive more pollen than those off mounds, and outcrossed flowers produce more seeds. Other small annuals in the same meadows (such as Lasthenia californica) appear to do much better in undisturbed areas.
We were interested in pursuing questions such as how disturbance affects plant color and how this may influence pollinator visits, whether levels of disturbance from year to year are sufficient to maintain this small population, and whether the effects of gopher mounds are due to reduced competition, nutrient availability, etc. |
Interaction of induced resistance and herbivore movement: spatial distribution of herbivores, plant damage and plant resistance
Collaborator: Dr. Kurt Anderson ; Funded by USDA
Induced resistance is a type of phenotypic plasticity in which plants change their level of resistance to herbivores in response to herbivore damage. By definition inducible resistance adds a source of variance to the interaction between plants and their herbivores. The temporal variability of inducible resistance can affect temporal herbivore population dynamics, and it has been predicted that induced resistance should also affect spatial variance in distributions of herbivores and damage to plants. Because many herbivores can move away from plants of low quality, herbivore movement should mediate the interaction of induced resistance with spatial distributions of herbivores, herbivore damage and plant resistance. To test these ideas, we used models and experiments using tomato and a pest caterpillar (Spodoptera). |
Natural history of the frosted elfin butterfly in the Apalachicola National Forest
Collaborators: Dr. Andrew Merwin, and Sally and Dean Jue, citizen scientists
Long-term monitoring of frosted elfin populations in the Apalachicola suggests that this locally rare butterfly may be declining and sensitive to fire management regimes on the forest. Our lab is assisting with analysis of long-term data, and field studies of incidence of frosted elfin eggs and larvae on host plants in areas with different burn histories and forest structures. |